Compact Dual-Band Shared-Aperture Omnidirectional Biconical Antenna for Microwave and Millimeter-Wave Applications

This communication proposes a new dual-band shared-aperture omnidirectional biconical antenna operating at 2.4–4.2 GHz and 24–30 GHz. Choke stubs are added at the compact biconical radiating structure to improve the low band (LB) radiation pattern envelopes, without compromising the good omnidirectional radiation performance in the high band (HB). The LB feeding network is based on parallel plate waveguide (PPW) and the HB one is based on the E-plane power divider, and they are all embedded in the center of the entire antenna structure. An annular PPW diplexer is further used to combine the orthogonal polarization signals from these two feeding networks to excite the shared radiation aperture. With the benefits of the different electromagnetic (EM) modes propagating in the PPW and E-plane waveguide, the polarizations of the proposed omnidirectional antenna in different bands exhibit orthogonal characteristics, (i.e., LB: V-pol and HB: H-pol). To validate the design concept, a prototype is demonstrated. Experimental results show that the antenna has good impedance matching (
$\vert \text{S}_{11}\vert $
or
$\vert \text{S}_{22}\vert < -10$
dB) performance in both bands. Meanwhile, the amplitude fluctuations in omnidirectional radiation patterns are within 1.3 and 2.9 dB for LB and HB, respectively.